Development of anaerobic migrating blanket reactor (AMBR), a novel anaerobic treatment system

A novel anaerobic treatment system, the anaerobic migrating blanket reactor (AMBR), was developed after completing a parallel study with upflow anaerobic sludge blanket (UASB) and anaerobic sequencing batch reactor (ASBR) processes. Using sucrose as the main component of a synthetic wastewater, the AMBR achieved a maximum chemical oxygen demand (COD) loading rate of 30 g.l-1.day-1 at a 12-h hydraulic retention time (HRT). This resulted in a standard methane production rate (SMPR) of 6.51.l-1.day-1 and an average methane-based COD (MCOD) removal efficiency of 62.2%. A key element in granular biomass formation was migration of the biomass blanket through the reactor. Although a carbohydrate-rich wastewater was used, no separate pre-acidification was required for the AMBR, because of high mixing intensities and wash out of acidogenic bacteria. In contrast, the absence of pre-acidification created "bulking" problems (caused by abundant acidogenic bacteria at the surface of granules) in a UASB reactor, operated under conditions similar to that of the AMBR. As a result, a maximum COD loading rate and SMPR of 21 g.l-1.day-1 and 4.91.l-1.day-1 were achieved, respectively, for the UASB reactor at a 12-h HRT. These values were 18 g.l-1.day-1 and 3.71.l-1.day-1, respectively, for an ASBR at a 12-h HRT. Hence, the performance of the AMBR in treating a carbohydrate-rich wastewater was found to be superior in terms of maximum loading rate and SMPR.     

Pre-acidification in anaerobic sludge bed process treating brewery wastewater

The effect of pre-acidification on anaerobic granule bed processes treating brewery wastewater was the focus of a comparison study employing two configurations, (a) a single stage upflow anaerobic sludge bed (UASB) and (b) an upflow acidification reactor in series with a methanogenic UASB. The pre-acidification reactor achieved 20±4% SCOD removal and 0.08±0.003 L of methane produced per gram of SCOD removal at a hydraulic retention time (HRT) of 0.75–4 h. Butyric acid was not detected and short chain fatty acids (SCFAs) were mainly acetic and propionic acids. The acidification ratio was about 0.42±0.02 g SCFAs as COD/g of influent COD.

Both systems’ critical loading rate to achieve 80% COD removal was established at 34–39 kg COD/m³ of total sludge bed volume per day. SCOD removal efficiency of 90±3% was achieved by both systems at an organic loading rate of 25±1 kg COD/m³ of total sludge bed volume per day, indicating that the installation of an acidification reactor had no effect in terms of the maximum granular activity, biomass granulation and the settleability of granules. At an organic loading rate of 67 kg COD/m³ of total sludge bed volume per day at an HRT of 1 h, the series system outperformed the single UASB by a removal of 62 compared to 57%.     

Anaerobic biodegradability and treatment of grey water in upflow anaerobic sludge blanket (UASB) reactor

Feasibility of grey water treatment in an upflow anaerobic sludge blanket (UASB) reactor operated at different hydraulic retention time (HRT) of 16, 10 and 6h and controlled temperature of 30 degrees C was investigated. Moreover, the maximum anaerobic biodegradability without inoculum addition and maximum removal of chemical oxygen demand (COD) fractions in grey water were determined in batch experiments. High values of maximum anaerobic biodegradability (76%) and maximum COD removal in the UASB reactor (84%) were achieved. The results showed that the colloidal COD had the highest maximum anaerobic biodegradability (86%) and the suspended and dissolved COD had similar maximum anaerobic biodegradability of 70%. Furthermore, the results of the UASB reactor demonstrated that a total COD removal of 52-64% was obtained at HRT between 6 and 16 h. The UASB reactor removed 22-30% and 15-21% of total nitrogen and total phosphorous in the grey water, respectively, mainly due to the removal of particulate nutrients. The characteristics of the sludge in the UASB reactor confirmed that the reactor had a stable performance. The minimum sludge residence time and the maximum specific methanogenic activity of the sludge ranged between 27 and 93 days and 0.18 and 0.28 kg COD/(kg VS d).     

Characteristics of sludge developed under different loading conditions during UASB reactor start-up and granulation

Sludge characteristics available inside the reactor are of vital importance to maximize advantages of UASB reactor. The organic loading rate and sludge loading rate applied during start-up are among the important parameters to govern the sludge characteristics. Effects of these loading rates on the characteristics of the sludge developed are evaluated in six laboratory scale UASB reactors. The sludge characteristics considered are VSS/SS ratio of the sludge, sludge volume index, specific gravity, settling velocity and metal contents of the sludge developed under different loading rates. The experimental results indicate that, for developing good characteristics sludge, during primary start-up from flocculent inoculum sludge, organic loading rate and sludge loading rate should be in the range of 2.0-4.5 kg COD/m3 d and 0.1-0.25 kg COD/kg VSS d, respectively (chemical oxygen demand, COD). Proper sludge granulation and higher COD removal efficiency will be achieved by these loading rates.     

内循环UASB处理酒精废水及其颗粒污泥特性

针对传统UASB反应器在启动时颗粒污泥形成缓慢的问题,采用内循环UASB反应器作为厌氧单元对酒精废水进行处理。其以低负荷启动,启动完成后容积负荷为7.9 kg/(m3.d),对COD的去除率可达80%,整个试验阶段对NH3-N的平均去除率为16.38%。扫描电镜显示颗粒污泥中的优势菌开始为短杆菌,随着培养时间的延长则出现了球菌;而现有UASB反应器中颗粒污泥的优势菌为丝状菌。对沼气成分进行分析,CH4含量最高为81.61%,N2含量则随着颗粒污泥培养时间的延长由3.68%增加至18.59%。     

Effect of anaerobic reactor process configuration on useful energy production

The effect of reactor process configuration on anaerobic production of useful energy (hydrogen and methane) from a complex substrate was investigated for the following reactor systems: suspended growth, two-phase mixed, two-stage mixed, upflow anaerobic sludge blanket (UASB) reactor, and two-phase UASB. The mixed two-phase and two-stage configurations yielded the highest specific energy productions of 13.3 and 13.4 kJ/g COD fed, respectively. Reactor process configuration influenced microbial pathways in acidogenic reactors in that butyrate was the predominant volatile acid in phased configurations, whereas acetate was predominant in the staged configuration. The UASB reactor achieved the highest average daily energy production per reactor volume of 101 kJ/L reactor-d. All reactor configurations achieved high COD removals on the order of 99%. However, hydrogen represented only 3% of the total energy produced by the two-phase mixed and two-phase UASB configurations. Theoretical analysis revealed that the maximum specific energy production by the two-phase suspended-growth configuration is only 9% higher than that for a single-stage mixed reactor. Consequently, the production of hydrogen from complex substrates in these process configurations does not seem to be justifiable solely from an energy point of view. Instead, it is suggested that phased anaerobic systems should be considered primarily for improved process stability whereas resultant hydrogen production is of secondary benefit.     

Anaerobic biodegradation of aircraft deicing fluid in UASB reactors

A central composite design was employed to methodically investigate anaerobic treatment of aircraft deicing fluid (ADF) in bench-scale Upflow Anaerobic Sludge Blanket (UASB) reactors. A total of 23 runs at 17 different operating conditions (0.8% 1.6% ADF (6000-12,000mg/L COD), 12-56h HRT, and 18-36gVSS/L) were conducted in continuous mode. The development of four empirical models describing process responses (i.e. COD removal efficiency, biomass-specific acetoclastic activity, methane production rate, and methane production potential) as functions of ADF concentration, hydraulic retention time, and biomass concentration is presented. Model verification indicated that predicted responses (COD removal efficiencies, biomass-specific acetoclastic activity, and methane production rates and potential) were in good agreement with experimental results. Biomass-specific acetoclastic activity was improved two-fold from 0.23gCOD/gVSS/d for inoculum to a maximum of 0.55gCOD/gVSS/d during ADF treatment in UASB reactors. For the design window, COD removal efficiencies were higher than 90%. The predicted methane production potentials were close to theoretical values, and methane production rates increased as the organic loading rate is increased. ADF toxicity effects were evident for 1.6% ADF at medium organic loadings (SOLR above 0.5gCOD/gVSS/d). In contrast, good reactor stability and excellent COD removal efficiencies were achieved at 1.2% ADF for reactor loadings approaching that of highly loaded systems (0.73gCOD/gVSS/d).     

Effect of specific gas loading rate on thermophilic (55 degrees C) acidifying (pH 6) and sulfate reducing granular sludge reactors

The effect of the specific gas loading rate on the acidifying, sulfate reducing and sulfur removal capacity of thermophilic (55 degrees C; pH 6.0) granular sludge bed reactors treating partly acidified wastewater was investigated. A comparison was made between a regular UASB reactor and a UASB reactor continuously sparged with N(2) at a specific gas loading rate of 30 m(3)m(-2)d(-1). Both UASB reactors (upflow velocity 1.0 mh(-1), hydraulic retention time about 5h) were fed a synthetic wastewater containing starch, sucrose, lactate, propionate and acetate and a low sulfate concentration (COD/SO(4)(2-) ratio of 10) at volumetric organic loading rates (OLR) ranging from 4.0 to 49.8 gCODl(-1) reactord(-1). Immediately after imposing an OLR of 25 gCODl(-1) reactord(-1), the acidification and sulfate reduction efficiency dropped to 80% and 30%, respectively, in the UASB reactor. Both efficiencies recovered slowly to 100% during the course of the experiment. In the N(2) sparged reactor, both the acidification and sulfate reduction efficiency remained 100% following the OLR increase to 25 gCODl(-1) reactord(-1). However, the sulfate reduction efficiency gradually decreased to about 20% at the end of the experiment. The biogas (CO(2) and CH(4)) production rate in the UASB was very low, i.e. <3l biogasl(-1) reactorday(-1), resulting in negligible amounts (<20%) of H(2)S stripped from the reactor liquid. The total H(2)S concentration of the N(2) sparged UASB reactor effluent was always below 25 mgl(-1), but incomplete sulfate reduction kept the maximal H(2)S stripping efficiency below 70%.     

Integrated removal of nitrate and carbon in an upflow anaerobic sludge blanket (UASB) reactor: Operating performance

Denitrification and methanogenesis of a synthetic wastewater containing volatile fatty acids and nitrate were obtained in a single-stage process using an upflow anaerobic sludge blanket (UASB) reactor. The reactor was initially inoculated with methanogenic granular sludge and was gradually adapted to nitrate by increasing the nitrate concentration in the influent. Excess carbon not utilized for denitrification was converted to methane. During steady-state at a loading of 336 mg NO₃-N/l/d (24 mmol NO₃/l/d) and 6600 mg COD/l/d more than 99% removal of both nitrate and carbon was achieved. Batch experiments with biomass from the reactor showed that approximately 90% of the added nitrate was recovered as nitrogen gas indicating that true dentrification occurred. This was further verified from mass balances over the reactor. The granules changed appearance during the first 5 months of operation being fluffy and buoyant, probably reflecting changes in the microbial composition induced by the presence of nitrate. However, during the next two months more dense granules with good settling abilities gradually established in the system making this kind of combined process feasible in a UASB reactor. Characterization of the produced granules showed that while the mean diameter and density was comparable to granules from purely methanogenic systems, although the strength was lower.     

Anaerobic treatment of municipal wastewater at ambient temperature: Analysis of archaeal community structure and recovery of dissolved methane

Anaerobic treatment is an attractive option for the biological treatment of municipal wastewater. In this study, municipal wastewater was anaerobically treated with a bench-scale upflow anaerobic sludge blanket (UASB) reactor at temperatures from 6 to 31 °C for 18 months to investigate total chemical oxygen demand (COD) removal efficiency, archaeal community structure, and dissolved methane (D-CH₄) recovery efficiency. The COD removal efficiency was more than 50% in summer and below 40% in winter with no evolution of biogas. Analysis of the archaeal community structures of the granular sludge from the UASB using 16S rRNA gene-cloning indicated that after microorganisms had adapted to low temperatures, the archaeal community had a lower diversity and the relative abundance of acetoclastic methanogens decreased together with an increase in hydrogenotrophic methanogens. D-CH₄, which was detected in the UASB effluent throughout the operation, could be collected with a degassing membrane. The ratio of the collection to recovery rates was 60% in summer and 100% in winter. For anaerobic treatment of municipal wastewater at lower temperatures, hydrogenotrophic methanogens play an important role in COD removal and D-CH₄ can be collected to reduce greenhouse gas emissions and avoid wastage of energy resources.     

Performance of an up-flow anaerobic stage reactor (UASR) in the treatment of pharmaceutical wastewater containing macrolide antibiotics

The performance of an up-flow anaerobic stage reactor (UASR) treating pharmaceutical wastewater containing macrolide antibiotics was investigated. Specifically, it was determined whether a UASR could be used as pre-treatment system at an existing pharmaceutical production plant to reduce the antibiotics in the trade effluent. Accordingly, a UASR was developed with an active reactor volume of 11 L being divided into four 2.75 L stages. Each stage of the reactor was an up-flow sludge blanket reactor and had a 3-phase separator baffle to retain biomass. The reactor was fed with real pharmaceutical wastewater containing Tylosin and Avilamycin antibiotics and operated with step-wise increases in the reactor organic loading rate (OLR) from 0.43 to 3.73 kg chemical oxygen demand (COD) m(-3)d(-1), and then reduced to 1.86, over 279 days. The process performance of the reactor was characterised in terms of its COD removal, Tylosin reduction, pH, VFA production, methane yield and sludge washout. At a total hydraulic retention time (HRT) of 4 d and OLR of 1.86 kg COD m(-3)d(-1), COD reduction was 70-75%, suggesting the biomass had acclimated to the antibiotics. Furthermore, an average of 95% Tylosin reduction was achieved in the UASR, indicating that this antibiotic could be degraded efficiently in the anaerobic reactor system. In addition, the influence of elevated Tylosin concentrations on the UASR process performance was studied using additions of Tylosin phosphate concentrate. Results showed similar efficiency for COD removal when Tylosin was present at concentrations ranging from 0 to 400 mgL(-1) (mean removal over this range was 93%), however, at Tylosin concentrations of 600 and 800 mgL(-1) there was a slight decline in treatment efficiency at 85% and 75% removal, respectively.     

好氧颗粒污泥技术用于味精废水处理的研究

以厌氧颗粒污泥为接种污泥,采用人工模拟废水在SBR反应器内培养好氧颗粒污泥,35 d后颗粒污泥成熟,反应器对COD和NH4+-N的去除率分别高于95%和99%。采用该反应器处理味精废水,当COD、NH4+-N的容积负荷分别为2.4、0.24 kg/(m3.d)时,对COD、NH4+-N和TN的去除率分别在90%、99%和85%左右,且颗粒污泥未出现解体的现象。以厌氧颗粒污泥为接种污泥、味精废水为进水,在与上述相同条件下培养好氧颗粒污泥,经过60 d的培养,反应器内的污泥以絮状污泥为主,该系统对COD、NH4+-N和TN的去除率分别为85%、99%和70%。     

两相厌氧工艺处理高盐纤维素醚废水的研究

采用接种特定污泥的两相厌氧反应器处理高盐纤维素醚废水,重点考察了启动过程及其处理效果。试验结果表明,当产酸相的HRT为18 h时,其所能承受的最大容积负荷为8.18kg/(m3.d),此时其对COD的去除率为20%左右;当产甲烷相的HRT为24 h时,其所能承受的最大容积负荷为5.5 kg/(m3.d),此时其对COD的去除率为35%左右;产甲烷相对COD的去除率与产酸相出水的酸化度呈显著正相关。在产酸相进水COD为6 000 mg/L、产甲烷相进水pH值为7的条件下,当产酸相进水pH值为6、HRT为18 h及产甲烷相的HRT为48 h时,系统的处理效果较佳,出水COD为1 800 mg/L,对COD的总去除率可达70%左右。     

UASB处理低浓度城市污水的生产性研究

广东某城市污水处理厂采用UASB-好氧工艺处理低浓度城市污水，对UASB的实际处理效能进行了考察。结果表明，在试验的进水水质条件下，当UASB的水力停留时间为6h时，系统对COD和BOD5的平均去除率分别为50％和60％，对TP的去除率为15％～38％。当HRT由5．67h延长至10h时，出水VFA浓度会随之降低，而pH值则始终稳定在6．5～7．5，系统对COD和BOD5的去除率分别增加9％和19％，对溶解性COD和BOD5的去除率分别增加25％和24％。     

Effect of process configuration and substrate complexity on the performance of anaerobic processes

The roles of substrate complexity (molecular size of the substrate) and process configuration in anaerobic wastewater treatment were investigated to determine optimal methanogenic technology parameters. Five substrates (glucose, propionate, butyrate, ethanol, and lactate) plus a mixed waste (60% carbohydrate, 34% protein, and 6% lipids) were studied under five reactor configurations: batch-fed single-stage continuous stirred tank reactor (CSTR), continuously fed single-stage CSTR, two-phase CSTR, two-stage CSTR, and single-stage upflow anaerobic sludge blanket (UASB). The substrate feed concentration was 20,000 mg/L as COD. The solids retention time (SRT) and hydraulic retention time (HRT) in the CSTR reactors were 20 d, while HRT in the UASB was 2 d. All reactors were operated for at least 60 d (equal to 3SRT). Substrate complexity was observed to be less significant under two-phase, two-stage and UASB reactor configurations. Two-phase CSTR, two-stage CSTR, and single-stage UASB configurations yielded the lowest effluent chemical oxygen demands (130-550, 60-700, and 50-250 mg/L, respectively). The highest effluent chemical oxygen demands were detected when feeding glucose, propionate, and lactate to continuously fed single-stage CSTRs (10, 400, 9900, and 4700 mg/L COD, respectively) and to batch-fed single-stage CSTRs (11, 200, 2500, and 2700 mg/L COD, respectively). Ironically, the one stage CSTR--most commonly utilized in the field--was the worst possible reactor configuration.     

Process modeling and analysis of palm oil mill effluent treatment in an up-flow anaerobic sludge fixed film bioreactor using response surface methodology (RSM)

In this study, the interactive effects of feed flow rate (QF) and up-flow velocity (V up) on the performance of an up-flow anaerobic sludge fixed film (UASFF) reactor treating palm oil mill effluent (POME) were investigated. Long-term performance of the UASFF reactor was first examined with raw POME at a hydraulic loading rate (HRT) of 3 d and an influent COD concentration of 44300 mg/l. Extreme reactor instability was observed after 25 d. Raw POME was then chemically pretreated and used as feed. Anaerobic digestion of pretreated POME was modeled and analyzed with two operating variables, i.e. feed flow rate and up-flow velocity. Experiments were conducted based on a central composite face-centered design (CCFD) and analyzed using response surface methodology (RSM). The region of exploration for digestion of the pretreated POME was taken as the area enclosed by the feed flow rate (1.01, 7.63 l/d) and up-flow velocity (0.2, 3 m/h) boundaries. Twelve dependent parameters were either directly measured or calculated as response. These parameters were total COD (TCOD) removal, soluble COD (SCOD) removal, effluent pH, effluent total volatile fatty acid (TVFA), effluent bicarbonate alkalinity (BA), effluent total suspended solids (TSS), CH4 percentage in biogas, methane yield (Y M), specific methanogenic activity (SMA), food-to-sludge ratio (F/M), sludge height in the UASB portion and solid retention time (SRT). The optimum conditions for POME treatment were found to be 2.45 l/d and 0.75 m/h for QF and V up, respectively (corresponding to HRT of 1.5 d and recycle ratio of 23.4:1). The present study provides valuable information about interrelations of quality and process parameters at different values of the operating variables.     

Organic removal by denitritation and methanogenesis and nitrogen removal by nitritation from landfill leachate

A system consisting of a two-stage UASB and anoxic-oxic reactor was used to enhance COD and nitrogen removal from landfill leachate. To improve denitrification efficiency, the raw leachate with recycled final effluent was pumped into the first-stage UASB (UASB1) to carry out simultaneous denitrification and methanogenesis. The results over 180 d show that the maximum organic removal rate in UASB1 and UASB2 was 12.5 and 8.5 kgCODm(-3)d(-1) in the oxic zone of the A/O reactor, respectively. The COD and biochemical oxygen demand (BOD5) removal efficiency of the system was 80-92% and about 99%, respectively. Without controlling temperature (17-30 degrees C) and dissolved oxygen (0.5-4.0 mgL(-1)), the maximum NH4+-N removal rate was 0.68 kg NH4+-Nm(-3)d(-1), and about 99% of NH4+-N removal was obtained by nearly complete nitritation. The 81-93% total nitrogen removal was obtained by complete denitrification in the UASB1 and in the anoxic zone of the A/O reactor. Fluorescence in situ hybridization (FISH) analysis of the sludge samples from A/O reactor showed that ammonia oxidizing bacteria (AOB) consisted 4% of the eubacterium, while nitrite oxidizing bacteria (NOB) counted less than 0.2% of that. The study shows that the main factors achieving and maintaining nitritation are a proper range of free ammonia concentration obtained by dilution recycled final effluent that inhibits NOB but not AOB; effective control on aeration time by indication of "ammonia valley" on pH profile; and highly efficient denitrification and its reproducing alkalinity to result in pH above 8.5.     

Dispersion and treatment performance analysis of an UASB reactor under different hydraulic loading rates

Mixing and transport phenomena affect the efficiency of all bioreactor configurations. An even mixing pattern at the macro-level is desirable to provide good conditions for substrate transport to, and from, the microbial aggregates. The state of segregation of particulate material in the reactor is also important. The production of biogas in anaerobic reactors is another factor that affects mixing intensity and hence the interactions between the liquid, solid and gaseous phases. The CSTR model with some degree of short-circuiting, dead zones and bypassing flows seems to describe the overall hydrodynamics of UASBs. However, few data are available in the literature for full-scale reactors that relate process performance to mixing characteristics. Dispersion studies using LiCl were done for four hydraulic loading rates on a full-scale UASB treating domestic wastewater in Ginebra, Valle del Cauca, southwest Colombia. COD, TSS, and Settleable Solids were used to evaluate the performance of organic matter removal. The UASB showed a complete mixing pattern for hydraulic loading rates close to the design value (i.e. Q = 10-13l s(-1) and HRT=8-6 h). Gross mixing distortions and localised stagnant zones, short-circuiting and bypass flows were found in the sludge bed and blanket zones for both extreme conditions (underloading and overloading). The liquid volume contained below the gas-liquid-solid separator was found to contribute to the overall stagnant volume, particularly when the reactor was underloaded. The removal of organic matter showed a log-linear correlation with the dispersion number.     

Tannery effluent as a carbon source for biological sulphate reduction

Tannery effluent was assessed as a carbon source for biological sulphate reduction in a pilot-scale upflow anaerobic sludge blanket (UASB), stirred tank reactor (STR) and trench reactor (TR). Sulphate removals of between 60-80% were obtained in all three reactors at total sulphate feed levels of up to 1800 mg l(-1). Sulphate removal in the TR (400-500 mg SO4 l(-1) day(-1)) and UASB (up to 600 mg SO4 l(-1) day(-1)) were higher than those obtained in the STR (250 mg SO4 l(1) day(-1)). A change in operation mode from a UASB to a STR had a large impact on chemical oxygen demand (COD) removal efficiencies. COD removal rates decreased by 25% from 600-700 mg COD l(-1) day(-1) to 200-600 mg COD l(-1) day(-1). The TR had an average COD removal rate of 500 mg COD l(-1) day(-1). Large quantities of sulphide were produced in the reactors (up to 1500 mg l(-1)). However due to the elevated pH in the reactor, only a small amount was in the form of H2S and thus the odour problem normally associated with biological sulphate reduction was not present.     

Anaerobic sewage treatment in a one-stage UASB reactor and a combined UASB-Digester system

The treatment of sewage at 15 degrees C was investigated in a one-stage upflow anaerobic sludge blanket (UASB) reactor and a UASB-Digester system. The latter consists of a UASB reactor complemented with a digester for mutual sewage treatment and sludge stabilisation. The UASB reactor was operated at a hydraulic retention time of 6h and a controlled temperature of 15 degrees C, the average sewage temperature during wintertime of some Middle East countries. The digester was operated at 35 degrees C. The UASB-Digester system provided significantly (significance level 5%) higher COD removal efficiencies than the one-stage UASB reactor. The achieved removal efficiencies in the UASB-Digester system and the one-stage UASB reactor for total, suspended, colloidal and dissolved COD were 66%, 87%, 44% and 30%, and 44%, 73%, 3% and 5% for both systems, respectively. The stability values of the wasted sludge from the one-stage UASB reactor and the UASB-Digester system were, respectively, 0.47 and 0.36g CH(4)-COD/g COD. Therefore, the anaerobic sewage treatment at low temperature in a UASB-Digester system is promising.